This invention relates generally to field effect transistors and more particularly to field effect transistors adapted to linearly amplify signals with minimum distortion and operate at relatively high power levels.
As is known in the art, field effect transistors (FETS), such as gallium arsenide (G.sub.a A.sub.s) FETS have been used in a variety of applications to amplify radio frequency signals. Such devices operate in response to a modulating signal fed to the gate electrode of such device. This modulating signal changes the "depth" of the bottom edge of a depletion zone which is produced by such signal in the gate region of the device. The drain current flowing from the source region, through the gate region, to the drain region is related to the depth of the bottom edge of the depletion zone and hence is related to the modulating signal. Consequently, changes in the gate voltage produce changes in the drain current. The ratio of a small change in drain current produced by a small change in gate voltage when the source-gate potential is varied about a nominal operating level is defined as the transconductance, gm, of the device.
When such devices are to operate at relatively large power levels, i.e. near the saturation point of the device, the nonlinear dynamic transfer characteristic of the device produces distortions, such as third order intermodulation products, which limit the power handling capability of the device in linearly amplifying signals.